Which heart sound occurs when the mitral and tricuspid valves close at the onset of systole?

The heart sound that occurs when the mitral and tricuspid valves close at the onset of systole is known as S1. This sound marks the beginning of ventricular contraction and is often described as a "lub." The closure of these valves prevents blood from flowing back into the atria during systole and initiates the ejection of blood into the aorta and the pulmonary artery.

Understanding the temporal relationship of heart sounds helps in assessing cardiac function and can indicate various conditions. For instance, a pronounced or diminished S1 sound might reflect changes in contractility or valve function, which can be clinically significant. In contrast, the other heart sounds (S2, S3, and S4) are associated with different cardiac events, such as the closure of the aortic and pulmonic valves (S2) or diastolic filling of the ventricles (S3 and S4). Recognizing S1 is crucial in both clinical practice and cardiology assessments.